Air-conditioning system



July 14, 1942. w MlLLER 2,289,923

AIR-CONDITIONING SYSTEM Filed NOV. 18, 1935 3 Sheets-Sheet l COOLING COIL HIGH TEMPERATuRE THERMOSTATIC EXPANSION VALVE LOW- TEMPERATURE v PLAIN EXPANSION VALVE s 2| CONDENSER COMPRESSOR 37 3 RELATIVE 32 HUMIDITY- 'CONTROL 57 5 56 33 S55 I gvvuv/vvkyb Fig. I T fizyland R.Miller July 14, 1942. w. a. MlLLER AIR-CONDITIONING SYSTEM Filed Nov. 18, 1955 a sheets-sheet 2 mum ZMQZOO w. R. MILL ER AIR-CONDITIONING SYSTEM July 14, 1942.

Filed Nov. 18, 1935 3 Sheets-Sheet 3 CONDENSER 9 21 walavadlzfliZlt-rr 'thecooling and dehumidification of air.

Patented July 14, 1942 Wayland R. Miller, Chicago, Ill., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application November 18, 1935. Serial No. 50,291

' 21 Claims.

The present invention relates to the art of air conditioning and is particularly concerned with In order to obtain either a cooling action or a dehumidifying' action, cooling of one type or an-- other is necessary. In the case of coolingof air,

it is only necessary to reduce the temperature of the air itself and to remove some of the superheat from the moisture present in the air, providing the ultimate desired temperature of the air is not too far below the dew-point thereof.

In order to dehumidify air however, it is not only necessary to lower the temperature of the air aswell as to remove superheat from the moisture contained therein, but it is also necessary to condense the moisture contained in the air by re-.

- moving therefrom an amount of heat equal to the latent heat of vaporization. The amount of cooling necessary, therefore, t obtain a dehumidifyin action is much greater than is necessary for a cooling action only and'where dehumidification' is not desired.

' therefore, is the provision of an air conditioning system in which the temperature of a cooling coil or a plurality of cooling coils is varied as a result of fluctuations in the relative humidity of the space being controlled.

While it is desirable to maintain certain predetermined relative humidity conditions within a space, still the temperature of'the space should be the dominating controlling factor. In the sys'-.

tems of the present invention, provision is therefore made to permit dominating control of the cooling means by the space temperature when the space temperature becomes excessive and irrespective of the value of the relative humidity therein.

, A further object of the invention therefore is the provision of systems for varying of the cooling effect to which the air to be conditioned is tive humidity, but in which the cooling effect is increased irrespective of the relative humidity submitted, in accordance with variations in relaconditions if the space temperature becomes excessive.

In one form of the invention, the temperature of a cooling coil used for air conditioning purposes is either maintained relatively high or relatively low dependent upon both the temperature and the relative humidity of the air in the space being controlled. In this form of the invention, the coil is maintained at the relatively low temperature whenever the relative humidity rises above some predetermined value and is operated at the relatively high temperature whenever the relative humidity of the space to be controlled is at an intermediate value. In addition, the temperature of the cooling coil is maintained at the relatively low' value if the room temperature is excessive and irrespective of whether or not the relative humidity is high. Furthenno cooling whatsoever can be obtained if the space temperature becomes too low;

It therefore follows that a further objectof the invention is the provision of an air conditioning system in which a cooling coil is selectively operated at a relatively high temperature, or at a relatively low temperature dependent". upon whether cooling or dehumidification is primarily desired.

It is a further object of the invention to maintain a relatively low temperature of the cooling coil in the event the temperature of the space becomes excessive and .to prevent any cooling if the space temperature becomes too low.

In a further modification of the invention, variable back'pressures are maintained ina cooling coil in accordance with fluctuations in the relative humidity of a space being supplied with air from a conditioner in which the cooling coil forms a part. In this form of the invention, the temperature of such space is controlled by permittirig more or less of the conditioned air to be diverted or by-passed. around the cooling coil. Provision is also made to maintain a relatively low back pressure on the cooling coil in the event the room temperature becomes excessive. The variable back pressure is maintained on the cooling coil in this form oftheinvention by variably positioning'a throttling valve which is located in the return pipe of the cooling coil. Control of the compression means for the refrigerating system that supplies the refrigerant to the cooling coil is then obtained by means responsive to the pressure in the return line between the throttling valve and the compressor.

Another object of the invention therefore is the provision ofan air conditioning system in which variable amounts of dehumidification are obtained by varying the temperature of a cooling coil through the medium of a throttling valve whichis located in the return line from the cooling coil.

An additional object of the invention is the controlling of such a throttling valve by the temperature of the space to be controlled in the event such temperature becomes excessive while normally controlling the temperature of the space by diverting or by-passing variable amounts of air around the cooling coil and delivering such by-passed air as well as the cooled air to the space.

Another object of the invention is the controlling of the refrigeration means in accordance with the pressure between a throttling valve located in the return. line and the compression means.

In a still further form of the invention, control of the relative humidit of a space is affected by maintaining variable back pressures in a refrigeration system upon fluctuations in the relative'humidity of the space, such variable back pressures being obtained by directly controlling the refrigerating means or compression system in accordance with the back pressure in the system and varying the standard of the back pressure thus maintained upon fluctuations in relative humidity. In this form of the invention, control of the temperature is obtained by rendering varying numbers of cooling coils operative and, under excessive temperature conditions, by maintaining a low back pressure in the refrigeration system irrespective of the value of the relative humidity. Also, inthis form of the invention, no cooling or dehumidification can take place if the space temperature becomes too low.

A further object of the invention therefore is the provision of an air conditioning system in which the number of cooling coils in operation is varied according to the temperature of a space being controlled and in which the temperature of the cooling coils is varied in accordance with fluctuations in relative humidity in the space.

Other objects of theinvention will be found in the drawings, the detailed description and the appended claims.

For a more complete understanding of the invention, reference may be had to the following detailed description and the accompanying drawings, in which:

Fig. 1 discloses one system constructed in accordance with the present invention wherein the temperature of a cooling coil is maintained either at a relatively high value or at a relatively low value, depending upon the temperature and relative humidity conditions of a space to be controlled.

Fig. 2 is a showing of a modified system wherein variable back pressures are maintained on a cooling coil upon fluctuations in relative humidity in a space to be controlled and wherein temperature control is obtained by diverting or by-passing part of the air around such cooling'coil, and

motor l2.

chamber ID by means of a fan H which may be driven in any suitable manner, as by the electric This air is then passed to the room or space to be conditioned by means of a duct l3. The air passing through the air conditioning chamber l0 may be cooled and dehumidified in any desirable manner and, in the present embodiment of the invention, such cooling and dehumidification is shown as being accomplished by means of a cooling coil l4, located in the air conditioning chamber l0, which cooling coil is adapted to be supplied with refrigerant by a suitable mechanical refrigeration system.

This refrigeration system includes a compressor l5 that is driven by an electric motor l6.

Refrigerant is returned from the coil 14 to the' compressor l5 by means of a pipe l1. .This refrigerant is thereupon compressed after which it is passed to a condenser l8 by means of a pipe IS. The condenser l8 may be of any of the wellknown types and operates to liquify the compressed gaseous refrigerant delivered thereto by the compressor l5. This liquid refrigerant is then delivered to the cooling coil 14 through two different paths, both of which include pipes 20 and 2|. One of these paths include a plain expansion valve 22 of any well known construction which operates to maintain a constant pressure on the coil l4. As is well-known in the art,

such a plain expansion valve is in reality nothingv more than a pressure reducing valve which is,

operated by the pressure on its eduction side. The liquid refrigerant may also pass from pipe 2| to the cooling coil l4 through two series connected valves 23 and 24. The valve 23 may be any suitable type of on or off valve and is herein shown as comprising a solenoid valve. The valve 24 is a thermostatic expansion valve which may be of any usual construction and includes a thermostatic bulb 25 which responds to the temperature of the refrigerant leaving the coil M. The bulb 25 is herein shown as clamped to a pipe 26, by means of a clamp 21, the pipe 26 being connected to the end of the coil l4 and to pipe l1.

Whenever liquid refrigerant is available, if the solenoid valve 23 is closed, then refrigerant can pass through the coil l4 only by way of the plain expansion valve 22. This expansion valve is so set that the temperature of the coil M is maintained well below the dew-point temperature of the air passing thereover. If the solenoid valve 23 is open however, then liquid refrigerant can also pass through the coil M by way of the thermostatic expansion valve 24. Since the thermostatic bulb 25 thereof responds to the temperature of the refrigerant leaving the coil Hi, this valve may be and is set so that the coil I4 is always flooded and is maintained at a relatively high temperature which may well be above the dew-point of the air passing over the same or slightly below thedew-point thereof.

The generation or supplying of liquid refrigerant may be controlled in any desirable manner and is herein shown as controlled by starting and stopping the compressor motor 16. This compressor motor IE and the solenoid valve 23 are controlled by the cooperative action of a room or space responsive humidity controller, generally indicatedat 30, and a room or space responsive temperature controller, or thermostat, generally indicated at 3|.

The humidity responsive controller 30 comprises an actuator 32 that expands and contracts in response to changes in relative humidity and thereabove.

may well take the form of a plurality of strands of hair. One end of the actuator 32 is secured as indicated at 33 and its other end is connected to a suitable tension spring 34 .bymeans of a cable 35. The other end of tension spring 34 is suitably fixed as indicated at 36 whereby the actuator 32 is maintained under tension at all times. if A pair of switch carriers 31 and 38, which.

are respectively pivoted at 39 and 40, are secured to the cable 35 at points indicated at 4| and 42. The switch carrier 31 supports a mercury switch 43 which is arranged to be moved to circuit closed position when the relative humidity of the air to which the actuator 32 responds falls to some predetermined minimum. The switch carrier 38 supports a mercury switch, 44 which is so arranged that it moves to circuit closed position when the relative'humidity of the air to which the actuator 32 responds rises to some predetermined maximum. For the purposes of this explanation, it will-be assumed that the mercury switch 43 is in closed circuit position for all relative humidity values below 50% and is in open circuit position for all relative humidity values the mercury switch 44 is closed when the relative humidity rises to 60% and is opened for a relative humidity values therebelow.

The temperature responsive thermostat 3| includes an actuator 45 which is herein shown as comprising a bimetallic element having one of its ends fixed as indicated at 46. The other 'end of bimetallic element 45 controls three switch arms 41, 48 and 49 which respectively cooperate with three relatively fixed contacts 50, and 52. The arrangement is such that switch arm. 41 first engages contact 50, then switch arm 48 engages contact 5| and thereafter switch arm 49 engages'contact 52 as the temperature to which actuator 45 responds increases. For the purposes of this explanation, it will be assumed that switch arm 41 engages contact 50 when the temperature rises to 72 F., the switch arm 48 engages contact 5| when'the temperature rises to 75 F., and the switch arm 49 engages contact 52 when the temperature rises to 78 F. It will be understood that the. temperature values set forth. for the temperature responsive device 3| and the relative humidity values set forth for the relative humidity control 30 may be varied Likewise, it will be assumed that had. These conditions of temperature and humidity are the desired normal conditions.

If the relative humidity of the room-0r space to be controlled shouldrise to 60%, then mercury switch 44 will be moved to closed circuit position, it being noted that mercury switch 43 i will thereby be opened; Opening of mercury the space or room to be controlled-and, if the plain expansion valve 22 since the solenoid valve 23 has been deenergized. The expansion valve 22 will thereupon maintain a pressure upon the coil M such that the temperature thereof will be well belowthe dew-point temperature of the air passing thereover. This air is therefore not only cooled but the moisture therein is condensed so as to lower its relative humidity. The relative humidity of the room or space to be controlled is thereby lowered. This cooling of the air below its dew-point will also result in cooling of temperature thereof drops below 72 F., the

switch arm 41 of the temperature controller 3| will disengage contact 50 whereupon the. circuit I for compressor motor It will be interrupted. In

this manner, no more liquid refrigerant will be furnished to the cooling coil l4 so that no further cooling or dehumidification of the air passaccording to the conditions of any particular installation and that the examples given herein above are merely illustrative.

Operatiqn of the system of Fig. 1

With the parts in the position shown, the relative humidity of the space to be controlled is.

below 50% so that the mercury switch 43 is closed and the mercury switch 44 is open. Also, the temperature of the space to be controlled is between 72 F. and .75 F. so that switch arm 41 is in engagement with contact 50 but the switch arms 48 and 49 are disengaged from their respective contacts 5| and 52. Under these conditions,

- the solenoid valve 23 is energized by a circuit as for cooling purposes and no appreciable" ing thereover can be accomplished. Thus, the switch comprised by switch arm 41 and contact 50 operates as aminimum temperature control to prevent a lowering of the temperature of the room or space to be controlled below some desired minimum irrespective of the relative humidity.

Now if the relative humidity should return to 50% or the'rebelow so as to again open mercury switch 44 and reclose'mercury switch 43, and if the temperature of the room or space rises to 75 F., so as to move switch arm 41 into engagement with contact 5|, then solenoid valve 23 will again be energized by the circuit set forth above and, in addition, the compressor motor I6 will be energized by a circuit as follows: line wire 55, wire 6|, bimetallic element 45, switch arm 48, contact 5|, wire 56, wire '64; compressormotor l6, and wire 65 to line wire 60. The compressor |5 is thereuponagain operated to furnish liquid refrigerant and this refrigerant now passes to the cooling coil l4 through the thermostatic expansion valve 24. The bulb 25 of thefishermostatic expansion valve 24, in responding to the temperature of the refrigerant leaving the cooling coil l4, maintains the cooling coil temperature relatively high and perhaps above the dewpoint of the air passing thereover whereby the refrigeration will be used substantially entirely dehumidification will take place.

If this should result in a rise in relative humidity so that the relative humidity again rises above 50%, then the mercury switch 43' will be opened. This opening of mercury switch 43 will deenergize solenoid valve 23 whereupon the cooling coil M will be controlled by the plain expansion valve 22 so that the temperature of cooling coil I4 will be lowered below the dew-point temperature of the air passing thereover. Under these conditions, a dehumidifying action as well as some cooling will be obtained. The proportion of cooling and dehumidification that is obtained under these conditions will depend on how far below the dew-point temperature of the air passing over the coil I4 the temperature of such coil is maintained.

If the temperature of the room or space to be controlled should rise to 78 F. so that switch arm 49 is brought into engagement with contact 52, then the solenoid valve 23 will be energized and the compressor motor I6 will be operated irrespective of the relative humidity. This energizing circuit for the solenoid valve 23 is as follows: line wire 55, wire 6|, bimetallic element 45, switch arm 49, contact 52, wire 61, wire 58, solenoid valve 23 and wire 59 to line wire 60. Therefore, under conditions of excessive temperature, the cooling coil I4 is maintained at a high temperature so that the whole effect of the refrigeration apparatus, or the greater part thereof, is utilized in cooling such air and substantially none of it is utilized in dehumidification. In this manner, the temperature of the room or space to be controlled can be maintained below an undesired maximum irrespective or the relative humidity conditions.

To recapitulate, the compressor motor I6 is operated whenever the room temperature rises to 75 F. and closes the switch defined by switch arm 48 and contact 5|. uid refrigerant thus supplied is utilized entirely for cooling or both for cooling and dehumidification depends upon the relative humidity. If the relative humidity is at 50% or therebelow, the mercury switch 43 is closed so that solenoid valve 23 is opened and under these conditions all cooling will be effected. On the other hand, if the relative humidity is above 50% so that mercury switch 43 is opened, then solenoid valve 23 will be deenergized and the coil I4 will be maintained below the dew-point of the air passing thereover so that dehumidification is effected, of course, being accompanied by a certain amount of cooling. If the relative humidity becomes excessive by rising to 60% or thereabove, the compressor motor I6 is operated even though the room temperature is below 75 F. but when switch arm 41 moves from engagement with contact 50 no further dehumidification can take place since the compressor motor I6 is thereby deenergized. Further, if the room temperature reaches some excessive value such as 78 F., the compressor motor I6 is operated and the solenoid valv 23 is opened irrespective of relative humidity conditions so that only cooling can be obtained to the exclusion of dehumidification.

Turning now to Fig. 2, a modified system is shown wherein a room or space to be conditioned is indicated at 10. Air is withdrawn from the room 10 and passed through an air conditioning chamber 1I after which it is delivered back to the room 10 by means of a delivery duct 12. This circulation of air may be obtained in any desired manner and is herein shown as being produced by means of a fan 13 which is driven by an electrical motor 14. The air conditioning chamber 1| is provided with a partition 15 which divides the chamber 1I' into a cooling chamber 16, and a by-pass chamber 11.

Located in the cooling chamber 16 is a cooling coil 18. A compressor 19, which is operated by an electrical motor 80, serves to compress refrigerant which then passes to a condenser BI after Whether or not the liqwhich it passes through a plain expansion valve 82 and to the cooling coil 18. A return line 83, by means of which the refrigerant is returned from the cooling coil 18 to the compressor 19, is provided with a throttling valve 84 which is controlled by the pressure in the return line between the throttling valve 84 and the cooling coil 18, the position of valve 84 also being modified in accordance with variations in the relative humidity of the space 10.

This valve 84 is provided with the usual valve stem 85 to which a rack 86 is secured. This rack 86 is driven by a pinion 81 which is secured to the final shaft 88 of a motor mechanism generally indicated at 89. This final shaft or main operating shaft 88 of the motor mechanism 89 is connected to a rotor shaft 90 through a speed reducing and torque amplifying gearing generally indicated at 9I. Secured to the rotor shaft 90 is a pair of motor rotors 92 and 93 with which are associated field windings 94 and 95.

Operative energization of the field windings 94 and 95 is controlled by a relay mechanism that includes a pair of relay coils 96 and 91 which operate to position a single plunger 98. The coils 96 and 91 may take the form of a single long coil provided with a center-tap or may be in the form of separate coils which are connected together in series. The plunger 98 positions a switch arm 99 to which it is connected by a non-conducting and non-magnetic connection I00. The switch arm 99 in turn cooperates with a pair of spaced contacts IOI and I02, the arrangement being such that switch arm 99 engages contact IOI if relay coil 96 is energized sufliciently'more highly than relay coil 91 and engages contact I02 if relay coil 91 is energized sufliciently more highly than relay coil 96.

The energizations of relay coils 96 and 91 are maintained substantially equal at all times, or are immediately substantially equalized in the event their energizations are unbalanced, by means of a balancing potentiometer which comprises abalancing resistance I03 and a cooperating balancing contact arm J04 which is driven by the main operating shaft 88 of the motor mechanism 89.

. tween the throttling valve 84 and the cooling coil 18 by means of a pipe I08. The pressure thus developed in the bellows I01 is opposed by a coiled spring I09 which has one of its ends secured to the actuating arm I06 and its other end secured to a suitable support I I0 which also supports the bellows I01. This bell-crank is pivoted at III and further includes a control arm I I2 and a corrector arm H3. The control arm I I2 cooperates with a control resistance H4 and the corrector arm II3 cooperates with a corrector resistance I I5. I

The action of the pressure responsive controller I05 upon the relay coils 96 and 91 is arranged to be modified by a compensating control responsive to-the relative humidity of the space 10. This relative humidity responsive compensating control is indicated generally at H1 and includes a bell-crank pivoted at II8. This bell-crank includes an actuating arm I I9 and a compensating arm I20 which cooperates with a compensating -19 lowers.

compensator as well as to the relay mechanism by means of a step-down transformer I30 having a high voltage primary I3I and a low voltage secondary I32. The relay coils 96 and 91, in series, the control resistance H4 and the compensating resistances I2I are all connected in parallel across the secondary I32 by means of wires I33 to I42 inclusive. Similarly, the balancing resistance I03 is connected across the secondary I32 by means of wires I43 and I44. The center of corrector resistance H is connected to the junction of relay coils 96 and 91' by wires I45, I46 and I41. The compensating arm I20 of the compensating control H1 is also connected to the junction of relay coils 96 and 91, through an adjustable rheostat I48, by wires I49, I50, I46 and I41. Similarly, the balancing contact arm I04 is connected to the junction of relay coils 96 and 91 through a manually adjustable rheostat I5I, by means of wires I52, I53 and I41. The field windings 94 and 95, in series, are connected across the secondary I32 by wires I33, I54, I55 and I42. The junction of the field windings 94 and 95 is connected to the switch arm 99, through a resistance I56, by wires I51 and I58. The contact I6I is connected to a small number of turns of the relaycoil 96 by a wire I59 and the contact I02 is similarly con-,- nected to a small number of turnsof the relay coil 91 by a wire I60. As will be explained more in detail hereinafter, the pressure responsive controller I05 operates to maintain a constant pressurein the return line between the throttling valve 84 and the cooling coil 18. The valve of this constant pressure thus maintained is lowered and raised by the relative humidity responsive compensating control H1 as'the relative humidity of the space increases and decreases. vThe com- I pressor motor 80 in this particular embodiment of the invention is then controlled by the pressure in the return line between the throttling valve 84 and the compressor 19. In this paraction of a spring I16. The switch carriers I69,

I12 and I respectively, support mercury switches I11, I18 and I19, the arrangement being such that these mercury switches sequentially move to open circuit position in the order named as the pressure in the return line be-- tween the throttling valve 84 and the compressor These mercury switches control the speed of compressor motor 80 through the mediand the control arm I95 is connected thereto by at I92.

. temperature.

um of a three-speed starting or control boi: I80. In order to control the temperature of the room or space 16, more or less air is by-passed or diverted around the cooling coil 18 by means of a by-pass damper I85. This by-pass damper I85 is located in the by-pass chamber 11 and is secured to a pivoted shaft I 86 to which a crank I81 is also secured. This crank I 81 is connected to a similar crank or lever I88 by means of a connecting link I 89. The crank or lever I88 is secured to the final driving shaft I90 of a motor mechanism I9I which may take the general form of the motor mechanism 89. The motor mechanism I9I is controlled by a :single potentiometer controller responsive to the dry bulb temperature of the space 10 which is indicated This temperature, responsive controller I92 includes a bell-crank pivoted at I93 which is provided with an actuating arm I 94 and a control arm I95. The actuating arm I94 is positioned by a bellows I96 that is charged with a suitable volatile fluid so as to be responsive to The variable pressures created in the bellows I96 are opposed by a' coiled spring I91 which has one of its ends connected to the actuating arm I94 and its other end connected to a" suitable support I98. The support I98 also serves to mount the bellows I96. The control arm I 95 cooperates with a control resistance I99. The ends of control resistance I99 are connected to the motor means I9I by wires 200 and 20I a wire 202.

Under conditions of excessive dry bulb temperature in the space 10 it may be desirable to operate the cooling coil 18 at its lowest temperature in order to greatly reduce the dry bulb temperature even'though the relative humidity is not unduly high. For this purpose, a switch carrier 205 is provided that lies in the path of movement of the crank or lever I 88 which is operated by the motor means I9I. This switch carrier 205 supports a mercury switch 206 that is normally biased to an open position by means of a compression spring 201 which has one of its ends abutting the underside of the switch carrier 205 and its other end abutting a suitable support 208; One terminal -of this mercury switch 206 is connected to the junction of relay coils 96 and 91 by being connected to the wire I45 by means of a wire 209. The other terminal of this mercury switch 206 is connected to the left-hand end of relay coil 96 by being connected to the wires I31 by means of a wire 2I0.

Operation of the system of Fig. 2

In the system of Fig. 2, the fan motor 14 continuously drives fan 13 to cause a continuous circulation of air from the space 10 through the air conditioner and'back to the space. With the parts in the position shown, the relative humidity of the space is at an intermediate value so the pressure controller I05 operates to maintain an intermediate pressure inthe return line.

In of the compensating control H1 is engaging the center of compensating resistance I2I. Under these conditions, the main operating shaft 88 is in intermediate position in which the throt-- tling .valve 84 is half open and the balancing contact arm I04 is engaging the center of balancing resistance I03. As a result, the relay coils 96 and 91 are substantiall equally energized and ,the switch arm 99 is intermediate contacts WI and I02. The field windings 94 and 95 are therefore connected in series across the secondary I32 and are equally energized. The two rotors 92 and 93 oppose each other and by reason of the fact that their respective field windings are equally energized, the rotor shaft 90 remains stationary.

If the pressure in return line 83 between the throttling valve 84 and cooling coil I8 should now decrease to a slight extent, the control arm H 2 of the pressure controller I will move along control resistance II4 towards the right-hand end thereof. This movement of the control arm II2 changes the voltage drops across relay coils 96 and 91 so that the relay coil 96 becomes more highly energized than the relay coil 91. When this difference in energization is sufficient due to a sufficiently large drop in pressure, plunger 98 will move to the left far enough to bring switch arm 99 into engagement with contact IN. This establishes acircuit through resistance I56. and the small number of turns of re- I lay coil 96, placing them in parallel with the field winding 95. The circuit for field windings 94 and 95 is then as follows: from the right-hand side of secondary I32, wire I42, wire I55, through field winding 94, whereupon the circuit branches,

one portion going by way of field winding 95,

wire I54, and wire I33 to the left-hand side of secondar I32 whereas the other portion goes by way of wire I5I, resistance I56, wire I58, switch arm 99, contact IOI, wire I59, the small number of turns of relay coil 96, wire I34, and wire I33 to the left-hand side of secondary I32. The field winding 94 is now energized more highly than the field winding 95 whereupon the rotor 92 overpowers the rotor 93 and moves the main operating shaft 88 in counter-clockwise direction as viewed from the left. Such movement of the main operating shaft -88 causes a downward movement of rack 86 and a consequent closing movement of the throttling valve 84. This movement of the main operating shaft 88 also causes balancing contact I04 to move downwardly along balancing resistance I03 towards its lower end. The energization of the small number of turns of relay coil 96 creates an additional pull on plunger 98 which causes switch arm 99 to engage contact IOI more firmly. When this counter-clockwise rotation of main operating shaft 88 has been sufficient, the movement of balancing contact arm' I04 downwardly along balancing resistance I03 again substantially equalizes the voltage drops across the relay windings 96 and 91 so as to substantially equalize the current flows therethrough. Plunger 98 therefore moves to the right and slightly separates switch arm 99 from contact IOI. This interrupts the circuit through the resistance I56 and the small number of turns of relay winding 96 so as to remove the addi- -tional attractive force on plunger 98 and cause a relativel wide separation of switch arm 99 and contact IOI and again places the field windings 94 and 95 in series across the secondary I32. Further rotation of the main operating shaft 88 will therefore cease.

In this manner, a reduction in the pressure between the throttling valve 84 and cooling coil I8 causes a partial closure of this throttling valve 84 so that the suction action of the compressor upon the cooling coil is reduced. This pressure will therefore tend to rise. If the pressure falls sufficiently, the throttling valve 84 will be completely closed.

On the other hand, a rise in this pressure causes movement of control arm II2 along control resistance II4 towards its left-hand end. This causes an increase in the voltage drop across the relay coil 91 over that across the relay coil 96 wherefore the plunger 98 tends to move to the right. When the pressure'has arisen sufficiently, switch arm 99 engages contact I02.-

The resistance I56 and the small number of turns of relay coil 91 are then placed in parallel with the field winding 94, the circuit for field windings 94 and 95 and these other parts being as follows: from the left-hand end of secondary I32, wire I33, wire I54, and through field winding 95, whereupon the circuit branches, one part going by way of field winding 94, wire I and wire I42 to the right-hand end of secondary I32, whereas the other portion goes by way of wire I5'I, resistance I56, wire I58, switch arm 99, contact I02, wire I60, the small number of turns of relay coil 91, wire MI, and wire I42 to the righthand end of secondary I32. The rotor 93 now overpowers the rotor 92 and drives the main operating shaft 88 in the reverse direction to move the throttling valve 84 towards open position and to move balancing contact arm I04 upwardly along balancing resistance I03. The energization of the small number of turns of relay coil 91 increases the pull on armature 98 in a right-hand direction so as to hold switch arm 99 in firm engagement with contact I02. When the main operating shaft 88 has thus moved sufficiently far, the voltage drops across relay coils 96 and 91 will again be substantially equalized so that plunger 98 returns to the left just far enough to separate switch arm 99 from contact I02. The field windings 94 and 95 are thus again placed in series across the secondary I32 and further movement of main operating shaft 88 ceases.-

The'deenergization of the small number of turns of the relay coil 91 removes the additional attractive force on plunger 98 wherefore switch arm- 99 separates appreciably from contact I02.

The function of resistance I56 is in the nature of a protective resistance to limit the amount of current flowing through the field windings 94 and 95 when the series parallel circuits described above are set up due to engagement of switch arm 99 with its cooperating contacts HM and I02. The function of the rheostat I5I is to interpose sufficient resistance in the balancing circuit to necessitate a relatively large movement of main operating shaft 88 in response to a relatively small movement of the control arm II2 of the pressure responsive controller I05. In this manner, a complete movement of main operating shaft 88 from valve open position to valve closed position and vice versa is obtained upon movement of control arm II2 over only a portion of the control resistance II4. In other words, the operating differential of the controller I05 is less than the complete operating range thereof.

The compensating controller I I1 serves to shift the operating range of the controller I05 within its total range of movement. With the relative humidity at an intermediate point, as shown in the drawings, so that the compensating arm I20 is engaging the center of compensating resistance I2I, the operating range of the controller I05 is in the middle of its total range. However, if the relative humidity should ri'se somewhat so that compensating arm I20 moves along compensating resistance I2I towards its right-hand end, the voltage drop across relay coil 98 is decreased in respect to the voltage drop across relay coil 91. As a result, the pressurein'the line between throttling valve 84 and cooling coil 18 must be reduced and cause movement of control arm II2 towards the right along control resistance H4 in order for the energizations of relay coils 98 and 91 to be substantially equal when the throttling valve 84 is half open. In this manner, a rise in the relative humidity in the space causes a shifting in the control point of the controller I05 so that a lower pressure is maintained between the throttling valve 84 and a higher pressure must be maintained on the suction side of the cooling coil 14 in order for the valve 84 to be half open; In this manner, the suction pressure on the cooling coil is reduced and increased as the relative humidity of the space rises above and falls below an intermediate desired value. In othervwords, the temclosing movement of the throttling valve 84 tends to further decrease the pressure in this line so that mercury switch I18 opens but mercury switch I19 is still closed. Mercury switch I19 controls a circuit through the three-speed control box that results in operation of compressor 80 at a relatively low speed. This circuit is as follows: line wire 2, wire '2I5, wire 2i8, wire 2I9, mercury switch I19, wire 220, three-speed control box I80, and line wire 2. If the pressure in this line should be further reduced, mercury'switch I19 will also open whereupon the compressor 80 ceases to operate.

In this manner, the pressure and therefore the temperature of the cooling coil 18 is varied in' conformity to variations in the relative humidity of the space and the compressor moperature of'the cooling coil 18 is reduced and increased upon rise and fall in relative humidity.

The function of the rheostat I48 is to enable the controller I05 to have dominating control of the motor means 89 even though the com-' pensating arm I20 of the compensating control I I1 moves to one of its extreme positions so that it directly engages either the wire I31 or the wire I38. If it were not for this rheostat, such engagement of the compensating arm I20 would cause a complete short-circu'iting of one-or the other of the relay coils 96 or 91 and the controller I05 would be unable to take dominating command. The function of the corrector resistance II5, a part of which is included in the control I circuit upon movement of the control arm H2 in either direction from the center of control resistance I I4, is not only to prevent complete short-cir'cuiting of either-relay coil 98 or 91 upon extreme movements of the controller I05 but also operates to maintain the operating differential of the controller I05 substantially constant irrespective of whether this operating range be in the middle or be shifted toward one or the oth r end of its total range of operation by reason of fluctuations in the relative humidity of the space.-

Whenever the valve 84 is relatively widely opened, the pressure in the return line between the valve 84 and the compressor 19 will tend to become quite high. Under these conditions. mercury switch I11 moves to closed positionand completes a circuit to the three-speed control box I80 which results in operation of compressor 80 at highspeed. This circuit is'as follows: line wire 2| I, wire 2I2, mercury switch I11, wire 2I3, three-speed control box I 80, and line wire 2I4. When the valve 84 is partially closed, the

action of compressor 19 will tend to reduce the However, under these con and through the by -pass chamber 11.

tor is operated at varying speeds in accordance with the load thereon.

In order to control the dry bulb temperature of the space 10, the dry bulb controller I92 vari- "ably positions the by-pass damper I85 to cause more or less air to flow around the cooling coil 18 As the dry bulb temperature decreases, the main operatinglshaft I of the motor means I9I rotates in a clockwise direction to lift link I89 and rotate by-pass damper I85 towards its horizontal position to allow more and more of the air being delivered to the space 10 to pass through the by-pass chamber 11 and mix with the cooled air so that the temperature of the space 10 is reduced to a less extent. On the other hand, as the temperature of the space rises, main operating shaft I90 of the motor mechanism I9I rotates in a counter-clockwise direction to move by-pass damper I85 towards its vertical position in which more and more of the air delivered to the space is caused topass over the cooling coil 18. This causes a decrease in the temperature of the space 10.

It is conceivable that under certain conditions, the relative humidity of the space may be fairly low so that the temperature of the cooling coil is maintained at a relatively high point. Under these conditions, if the space temperature should become excessive, the passing of all of the air delivered to the space over this cooling coil 18 might not cause the desired reduction in the space temperature. Means are therefore provided to cause a decrease in the temperature of the cooling coil 18 whenever the by-pass damper I85 moves 'to its vertical position. When the main operating shaft" I90 of the motor means I9I is rotated epunter-clockwise sufficiently far to move this lay-pass damper to its full vertical position, thenthe lever or crank I88 engages the switch carrier 205 and depresses the same against the action of the spring 201 so as to close themercury switch 206. Such closure of mercury switch 206 short-circuits the relay coil 98 and switch arm 99 engages contact I02 to open throttling valve 84 to its full open position. This causes the pressure in the line between throttling valve 84 and the compressor 19 to increase to a maximum and the compressor is therefore operated at full speed. As the result, maximum refrigerating action is obtained under these conditions to reduce the temperature of the space. A resistance 22I is preferably placed in the wire 2 I0 to prevent complete short- I circuiting of the relay coil 96.

In actual practice, the usual limit switches would be associated with the motor means 89 to determine the limits of movement of the main operating shaft 88 rather than depending upon a balancing outprocess by the balancing potentiometer comprised by the balancing resistance I83 and balancing contact arm I84. For a more complete understanding of the manner in which the motor mechanism 89 is controlled by a controller and a compensator, reference may be had to the copending application of John E. Haines, Ser. No, 38,946, filed September 3, 1935. It is thought from the above description that the manner in which the motor means l9| is controlled by a single potentiometer controller I92 should be evident. However, instead of providing a motor means l9| of the electrically balanced type, this control system may well take the form shown in Cunningham Patent No. 1,989,972 which issued February 5, 1935.

Turning now to Fig. 3 of the drawings, a further modification is shown wherein a space to be conditioned is indicated at 225. An air conditioning chamber indicated at 226 is connected to the space 225 by a delivery duct 221. Any suitable means, such as the fan indicated at 228, may be utilized to produce a flow of air through the air conditioning chamber 226 and into the space 225. As is usual in the art, the air supplied to the air conditioning chamber 226 may be taken from the outdoors or the space .225 or in predetermined mixtures of these two types of air under manual or any of the usual automatic controls. In this embodiment of the invention, instead of cooling the air varying degrees by maintaining the cooling coil at varying temperatures to obtain varying space temperatures, this is accomplished by rendering a varying number of cooling coils, over which the air must pass in series, operative. Specifically, the air conditioning chamber 226 is provided with three cooling coils indicated at 229, 238 and 23l. These cooling coils 229, 238 and 23l are all supplied with liquid refrigerant from a supply header 232 which is connected to a suitable condenser 233. Between the supply header 232 and the cooling coil 229,.there is interposed an electrically operable shut-off valve 234 and a thermostatic expansion valve 235 having the usual controlling bulb 236 which responds to the temperature at the outlet of the cooling coil .229. Similarly, the cooling coil 238 is connected to the supply header 232 through an electrically operable shut-01f valve 231 and a thermostatic expansion valve 238 which includes the usual controlling bulb 239 which responds to the temperature of the outlet side of the cooling coil 238. In exactly the same manner, the cooling coil 23l is connected to the supply header 232 through an electrically operable shut-off valve 248 and a thermostatic expansion valve 241 that is provided with a control bulb 222 which responds to the temperature of the cooling coil 23l at its outlet side.

The cooling coils 229, 238 and 23l all discharge into a common return header 242. In this embodiment of the invention, instead of having a single compressor that operates at varying speeds, a multiplicity of compressors 'are utilized which are brought into operation in sequence as the load increases. These compressors are indicated at 243, 244, and 245 and are all connected to the return header 242 and to the condenser 233. These compressors are respectively provided with compressor motors 246, 241 and 248.

In this instance, the compressor motors 246, 241 and 248 are energized in direct response to changes in the pressure in the return header 242. For this purpose, a motorized mechanism 249 is provided with an extended main operating shaft 258 which hasmounted thereon three cams 25I, 252 and 253. Cam 25l controls aswitch that includes a stationary switch arm 254 and a movable switch arm 255. Cam 252 controls a similar switch that includes a stationary switch arm.256 and a movable switch arm 251. Similarly, cam 253 controls a switch that includes a stationary switch arm 253 and a movable switch arm 259. With the parts in the position shown, the main operating shaft 258 is in one of its extreme positions and, under these conditions, the movable switch arms 255, 251 and 259 are all disengaged from their respective cooperating stationary switch arms 254, 256 and 258. The cam 25l is provided with an operating portion 223 which has a length corresponding substantially to the total range of movement of the main operating shaft 258. The cam 252 has an operating portion 268 of considerably shorter length and the cam 253 has an operating portion 26l of even shorter length. The arrangement is such that upon movement of main operating I shaft 258 from the extreme position in which it is shown towards its other extreme position, a relatively small amount of initial movement causes operating portion 223 of cam 25! to engage the movable switch arm 255 and move the same into engagement with switch arm 254. When the main operating shaft 258 has traveled about half of its movement, then the cam 252 brings its operating portion 268 into engagement with movable switch arm 251 to move the same into engagement with switch arm 256, and when the main operating shaft 258 has substantially completed its movement so that it approaches its opposite extreme position, then. the operating portion 26l of cam 253 engages switch am 259 and moves the same into engagement withswitch arm 258. In this manner, as the main operating shaft 258 travels from the one extreme position in which it is shown to its other extreme position, these three switches are sequentially closed. The first of these switches controls a circuit to compressor motor 246 which is as follows: line wire 262, wire 263, switch arm 255, switch arm 254 wire 264, compressor motor 246, wire 265, and line wire 266. Similarly, the second of these switches controls a circuit to compressor motor 241 which is as follows; line wire 262, wire 261, switch arm 251, switch arm 256, wire 268, compressor motor 241, wire 269, and line wire 266. Likewise, the last of these switches controls a circuit to compressor motor 248 which is as follows: line wire 262, wire 218, switch arm 259,

' turn header 242.

switch arm 258, wire 2", compressor motor 248, wire 212, and line wire 266. As the result, travel of main operating shaft 258 from the extreme position in which it is shown to its opposite extreme position sequentially energizes compressor motors 246, 241 and 248.

The positioning of the main operating shaft 258 by the motor mechanism 249 is controlled primarily by a controller generally indicated at 215 which responds to the pressure in there- This controller 215 includes a bell-crank having an operating arm 216 which is positioned by a bellows 211 that is connected to the return header 242 by means of a pipe 218. The pressures thus createdin the bellows 211 are opposed by a coil spring.219., This bellcrank further includes acontrol arm 288 and a corrector arm 28!, the control arm 288 cooperating with a control resistance 282 and the corrector arm 281 cooperating with a corrector resistance 283. The opposite ends of the control resistance 282 and th mid-portion of the corrector resistance 283 are connected to the motor means 249 by wires 284, 285 and 286. Associated withthe motor means 249 and its controller 215 is a manually operable rheostat 281 by which the amount of movement of control arm 280 in respect to its control resistance 282 required to cause a complete movement of main operating shaft 250 from one 'of its extreme positions to its other extreme position may be determined.

wire 335, switch arm 325, switch arm 324, wire 336, shut-ofl valve 231 and wire 331 to line wire 334. Likewise, the switch arms 328 and 321 control a circuit to shut-oil valve 240 which is as follows: line wire 330, wire 338, switch arm'328, switch arm 321, wire 339, shut-off valve 240 and wire 340 to line wire 334. With the parts in the position shown, the main operating shaft 316 is in one of its extreme positions. Upon a relatively small initial movement of this operating shaft 316 towards its other extreme position, the operating portion 320 of cam 311 moves switch arm 321 into engagement with switch arm 322 where- The setting of this rheostat 281 is such that only a small part of the total range of movement of the controller 215 is required to cause a complete movement of main operating shaft 250.

The particular portion of the total range of movement of controller 215 which will be effective to cause complete movement of main operating shaft 250 is determined by a compensating control, generally indicated at 290 which responds to the relative humidity of thespace 225. This compensating control includes a bell-crank which is pivoted at'291 and is provided with an operating arm 292 and a control arm 293. One end of a humidity responsive element 294 is secured to the operatingarm 292 and its other end by to energize shut-off valve 234 and move the same to open position. When the main operating shaft 316 has moved through about half of its range of movement, the operating portion 323 is secured to a suitable support 295. A coiled spring 296 has one of its ends secured to the compensating arm 293 and its other end secured to'a suitable support 291 and serves to'maintain the humidity responsive element 294 under proper tension. The compensating arm 293 cooperates with a compensating resistance 298. This com- 3 pensating resistance 298 is connected to the motor means 249- by means of wires 299 and 300. The compensating arm 293 is connected to the motor means 249 through a manually adjustable rheostat 301 and by means of wires 302 and 303. The manually operable rheostat 301 operates to maintain the controller 215 in dominating control of the motor mechanism 249 even though the compensating control 290 moves to one of its extreme positions.

The motor mechanism 249 is additionally controlled by a space temperature responsive thermostat that includes a bimetallic actuating element 305 which positions a contact blade 306 that is adapted to cooperate with a stationary contact 301. A This thermostat is connected to the motor mechanism 249 by wires 308 and 309. I Y

The electrically operable shut-off valves 234, 231 and 240 arecontrolled by the temperature of the space 225 through a motor mechanism 315. This motor mechanism drives a main operating shaft 316 to which is secured three cams 311, 318 and 319. The cam 311 is provided with an operating portion 320 of relatively long length which is arrangedto move a movable switch arm- 321 into engagement with alstationary switch arm 322. Similarly. the cam 318 is provided with an operating portion 323 of shorter length which is adapted to move a movable switch arm 324 into engagement with a stationary switch arm 325. Likewise, the cam 319 is provided with an operating portion 326 which is arranged to move a movable switch arm 321 into engagement with a switch arm 328.

The switch arms 321 and 322 control a circuit to shut-oil valve 224 as'follows: line wire 330, wire 331, switch arm 322, switch arm 321, wire 332, shut-off valve 234 and wire 333 to line wire 334. The switch arms 324 and 325 control a circuit to shut-01f valve 231 as follows: line wire 330,

ment with switch arm 325 whereupon shut-off valve 231 is-energized to open the same. Then,

when the main operating shaft 316 has nearly reached its other limit of movement, the operating portion 326 of cam 319 engages switch arm 321 to move the same into engagement with switch arm 328 whereupon the shut-off valve 240 is energized and moves towards open position. In this manner, progressive movement of the main operating shaft from the extreme position in which it is shown towards its other extreme position causes sequential energization and opening of the shut-oil valves 234,231 and 240.

The motor mechanism 315, and therefore the position of the main operating shaft 316, is conltrolled by a controller 350 which responds to the dry bulb temperature of the space 225. This controller-includes a bell-crank pivoted at 351 which is provided with an operating arm 352 and a control arm 353. The operating arm-352 is positioned by a thermostatic member herein shown in the form of a bellows 354 which is charged with a suitable volatile fluid so that varying pressures are generated therein upon temperature changes. A coiled spring 355' is arranged to oppose the variable pressures thus created in the bellows 354 and has one of its ends secured to the operating arm 352 and its other end secured to a suitable support 356 to which one end of bellows 354 is also secured. The control arm 353 ccoperates with a control resistance 351 which has its opposite ends connected to the motor mechanism 315 by wires 358 and 359. In addition, the operating arm 353 is also connected to the motor mechanism 315 by 'a wire 360.

Operation of the system of Fig. 3

so that all of the electrically operable shut-off valves 234, 231 and 240 are closed and no refrigerant can flow from the supply header 232 to any of the cooling coils 229, 230 or 231. In this manner, under extreme conditions wherein the dry bulb temperature reaches its low permissible limit, no cooling or dehumidifying action can take place. Also, an extreme relative humidity condition has been shown wherein the relative humidity of the space is at the lower limit of its desired range so that the compensating arm 293 of the compensating control 290 is engaging the extreme left-hand of compensating resistance 298. Under these conditions, the control point of the pressure responsive controller 215 has been shifted so that a high pressure will be maintained in the return header 242. If this pressure should increase too much, the bellows 211 will expand, and control arm 288 will move a little further along control resistance 282 towards its left-hand end so as to move main operating shaft 258 of the motor mechanism 249 towards its other extreme position and cause energization of the compressor motor 245. Inasmuch as all of the shut-off valves 243, 231 and 240 are closed, operation of this one compressor motor 246 would quickly reduce the pressure in the return header 242 and cause return movement of control arm 280 to the position shown wherein main operating shaft 250re'turns to its extreme position and deenergizes compressor motor 246.

Assuming now space 225 should rise somewhat, control arm 353 of the temperature responsive controller 350 will move along control resistance 351 towards its left-hand end and cause corresponding movement of main operating shaft 315 of the motor mechanism 3I5. A slight initial movement of this main operating shaft 3l6 moves switch arm 32I into engagement with switch arm 322 to energize the shut-off valve 234 which thereupon opens. Refrigerant therefore flows to the cooling coil 229 and this coil is filled with refrigerthat the temperature of the t sar y.

temperature of the space continues to rise. If

this happens, the control arm 353 of the temperature responsive controller 350 will continue to move along control resistance 351 towards its left-hand end so as to cause further rotation of main operating shaft 315 and finally move switch arm 324 into engagement with switch arm 325. Shut-off valve 231 is therefore energized and moves to open position whereupon refrigerant flows to the cooling coil 213. This cooling coil is filled with refrigerant under the control of the thermostatic valve 238. A further increase in the space temperature will result in further movement of main operating shaft M6 to its other extreme position to open shut-off valve 240 and cause the cooling coil 23 to be filled with If the relative humidity should increase, compensating arm 293 will move along compensating resistance 298 towards its right-hand end and thereby shift the control point of the pressureresponsive controller215 towards its right-hand end. The controller 215 will therefore operate the motor mechanism 249 to energize and deenergize compressor motors 246 and 241 and 248 in a manner to mantain a lower back-pressure in the return header 242 wherefore the cooling coils which are in operation will be maintained at lower temperatures. This lower temperature will cause the removal of more moisture from the air than the higher temperature therefore maintained so that more dehumidifying action will take place. With this lower coil temperature, the temperature of the space 225 may again fall to such an extent that only two or one, or perhaps an extreme condition will be reached, wherein none of the cooling coils .are in operation.

0n the other hand, if the relative humidity remains at the low value shown, and the temperature of the space becomes excessive even though all three cooling coils are in operation, then the contact blade 306 will be moved into engagement with contact 381 by the thermostatic element 305 and operate motor mechanism 249 to its other extreme position in which all of the com-' pressor motors 246, 241 and 248 are in operation. The pressure in return header 242 is therefore greatly reduced and the temperature of the cooling coils is reduced to provide the necessary amount of cooling action to return the temperature of the space 225 to within reasonable limits. Of course, this lower temperature of these cooling coils will result in greater dehumidification' even though such dehumidiflcation is not neces- From the foregoing; it will be seen that the system of Fig. 3 varies the temperature of the cooling coils according to the relative humidity in the space so that more or less dehumidification takes place, depending upon whether the humidity be high or low. In addition, the number of cooling coils in operation is controlled by space temperature so that if the space temperature is lower than desired, none of the coils can be placed in operation even though the relative humidity is higher than desired. 0n the other hand, all of the-coils are placed in operation and the temperature thereof is reduced to the lowest possible point even though dehumidification is not required in the event the temperature of the space becomes excessive. When the space temperature is between these extreme low and high values however, the temperature of the cooling coils depends at all times upon the relative humidity conditions in the space and the proper temperature ismaintained by bringing into operation the amount of coils necessary under the prevailing coil temperatures. The function of the thermostatic expansion valves 235, 238 and 2 is to maintain their respective coils full of refrigerant, rather than to vary the coil temperature.

From the foregoing, it will be seen that in this application, I have disclosed three different systems wherein refrigerating apparatus is' operated in the most economical manner so as to provide the desired cooling and dehumidifying effects while maintaining thetemperature to; be controlled in dominating control in that maximum cooling can be obtained irrespective of the relative humidity if the temperature of the space being controlled becomes too high. Further. in

some instances, no coolling at all can be obtained if the space temperature becomes too low. It

will be readily seen that many changes could be made in the systems disclosed herein and it is to be understood that these systems are merely exemplary of some of the forms which my invention may take. I intend therefore only to be limited by the scope of the appended claims.

I claim:

1. In an air conditioning system for a space, in combination, means to cool the air in the space comprising a direct expansion refrigeration system, space moisture responsive means in control of said cooling means to gradually increase the effect thereof as the moisture content in-- creases, and. means responsive to the temperature of the space to increase the cooling effect of the cooling means to a maximum if the space temperature becomes too high and to prevent any cooling of the air if the space temperature becomes too low, irrespective-of the moisture content of the air. 2. In an air conditioning system for a space, in combination, a cooling coil, variably positionable motor means, mean controlled thereby to lower the temperature of said coil, means responsive to the moisture content of the space to variably position said motor means, and a switch controlled by space temperature associated with said motor means operable to cause the-same to maintain said coil at a predetermined temperature irrespective of the moisture content of the space if the space temperature becomes too high.

3. An air conditioning system of the class described, comprising, in combination, a cooling coil over which air to be conditioned is passed before deliverin the same to a space to be controlled, compressor means for supplying refrigerant to said coil an expansion valve in control of the fiow of refrigerant to said coil, a throttling valve in the outlet conduit for said coil and in control of the refrigerant from said coll, motor meansto variably position said throttling valve, means'responsive to changes in moisture content in said space controlling said motor means to move said valve towards'closed'position as the humidity rises and vice versa, damper means arrangedto .by-pass air around said c011,, motor means in control of said damper means, and a.

device controlled by the temperature in said space in control of said last-named motor means.

4. An air conditioning system for a space, comprising, a cooling coil for CCOliIlg the space, a

compressor to supply refrigerant to said coil, a

throttling valve in control of the flow of refrig-.

erant from said coil, electric motor means in control of said valve, means responsive to the moisture content of the air in the space in'control of said motor means to variably position the same upon fluctuations in the moisture content 'of the air in the space, and a switch controlled by the temperature of the space to position said motor means and therefore said throttling valve in a predetermined position upon rise in space temperature to a predetermined value.

5. An air conditioning system for a, space, comprising, a cooling coil for cooling the space, a compressor to supply refrigerant to said coil, a throttling valvev in control of the flow of refrigerant from said coil, means responsive to the relative humidity of the space in control'of said throttling .valve to variably position the same upon fluctuations in the space relative'humidity,

cooling coil on the temperature of the space, mo-

tor means to variably position said damper means, space temperature responsive means to variably position said motor means. and means actuated by said motor means at a predetermined position thereof to additionally control said throttling valve.

6. In a moisture controlling system, in combination, a cooling coil to reduce the temperature of air passed thereover, compression means to supply refrigerant to said cooling coil, a throttling valve in control of the flow of refrigerant from said coil, a single motor means in control of said throttling valve, means responsive to the pressure in said coil in control of said motor means, and moisture responsive means to additionally control said motor means.

7. In an air COIidltiOliiIlg system, in combination, a plurality of cooling coils, moisture responsive means to graduatingly vary the temperature of said cooling coils, and means responsive to temperature. to determine the number of cooling coils to be placed in operation, and to also control the temperature of said coils.

8. An air conditioning system for a space, comprising, in combination, a plurality of cooling coils, a valve in control of each coil, variably poto sequentially open the same, means responsive to the temperature of the space to position said motor means, a secondvariably positionable motor means in control of the cooling effect of said coils, space moisture responsive means in control of said second motor means, and means controlled by space temperature controlling aid second motor means to lower the temperature of said coils if the space temperature becomes too high.

9. In an air conditioning system, in combination, a cooling coil to reduce the temperature of the air passed thereover, means to supply refrigerant to said cooling coil, means in control of the flow of refrigerant from the coil, a single motor in control of said last mentioned means, a single source of power for said single motor, means re sponsive to the pressure in the coil in control of the application of said power to said single motor,

and temperature responsive means to additionally control the application of said power to said damper means to determine the effect of said I single motor.

10. In an air conditioning system, in combination, a coolingcoil to reduce the temperature of the air passed thereover, means for upplying refrigerant to said coil, means for controlling the flow of refrigerant through said coil, a single motor in control of the last mentioned means, a

single source of power for said single motor,

means responsive to the pressure in the coil in control of the application of said power to said single motor, and moisture responsive means also in control of the application of power to said single motor.

' ll. In an air conditioning system, in combination, a cooling coil to reduce the temperature of the air passed thereover, means for supplying refrigerant to the coil, variable capacity means for reducing the back pressure on said coil, valve means for controlling the flow of refrigerant from the coil, said means being interposed between the coil and the back pressure reducing means, moisture responsive means in control of the valve means for graduatingly positioning the same, and

means responsive to the pressure between said ture in the space to a predetermined value for causing operation of the cooling means at a minimum temperature.

13. In an air conditioning system for a space, a plurality of cooling coils, individual electrically operated control valves for said coils, individual switches for said control valves, means for controlling the cooling effect of said coils, a first motor means for causing sequential actuation of said switches, a second motor means for controlling the cooling effectof said coils, and means responsive to the temperature humidity conditions of the space in control of one of said motor means and means responsive to one of said conditions in control of the other of said motor means.

14. In an air conditioning system, an air conditioning chamber for conditioning the air in a space, cooling means in said conditioning chamber, a variable capacity compressor means for circulatin refrigerant through said cooling means, a plurality of control devices for controlling the capacity of said compressor means, motor means for controlling the operation of the control devices, means responsive to the temperature of the space being conditioned in control of said motor means, and means responsive to the humidity of the space in control of said motor means, whereby the capacity of the compressor means is varied according to the temperature and humidity of the air in the space.

15. In an air conditioning system, an air conditionin chamber for conditioning the air in a space, cooling means in said conditioning chamber, a variable capacity compressor means for circulating refrigerant through said cooling means, a plurality of control devices for controlling the capacity of the compressor means, motor means for controlling the operation of the control devices, means responsive ot the humidity in the space being conditioned for controlling the motor means whereby the capacity of the compressor means is increased in a. series of steps as the humidity increases, and means responsive to the temperature of the space for causing operation of the motor means whereby the control devices cause high capacity operation of the compressor means regardless of the humidity in the space when the temperature therein is sufficiently.

high.

16. In an air conditioning system, an evaporator coil fcr cooling the air in a space, compressor means for supplying refrigerant to said coil, valve means controlling the flow of refrigerant from said coil to the suction side of said compressor means, means responsive to the pressure at the outlet of said evaporator coil for positioning said valve means in a, manner to maintain a substantially constant pressure at the outlet of said evaporator coil, and means including a variable resistance, the resistance of which is gradually varied in response to changes in one of the conditions of the air for graduatingly adjusting thepressure which is maintained at the outlet of said evaporator coil by said pressure responsivemeans.

17. In an air cooling and dehumidifying apparatus, the combination of evaporator means, compressor means of variable capacity, condensing means, and means operable automatically to effect operation of the compressor means at full capacity and to supply a maximum portion of the evaporator means with liquid refrigerant to produce a low temperature therein in response to a predetermined maximum temperature and independently of humidity, to effect operation of the compressor means at reduced ca-' pacity and to supply a reduced portion of the evaporator means with liquid refrigerant to produce an intermediate temperature therein in response to a relatively low humidity and a temperature intermediate said predetermined maximum temperature and a predetermined minimum temperature, and normally to effect operation of the compressor means at a sufficiently high capacity to produce a relatively low evaporator means temperature and to supply a reduced portion of the evaporator means with liquid refrigerant in response to a relatively high humidity and a temperature intermediate said predetermined maximum temperature and a predetermined minimum temperature.

18. In a refrigerating system, the combination of a plurality of refrigerant evaporators, a plurality of compressor elements for supplyin refrigerant to said evaporators means for condensing the compressedrefrigerant, means associated with the evaporators for respectively controlling the operation thereof, an electrical circuit, means influenced by a conditionbrought about by the operation of the controlling means for varying the value of a characteristic of the circuit, motor means including means responsive to said characteristic of the circuit, said motor means assuming positions corresponding to the value of said characteristic, means actuated upon movement of said motor means to a predetermined position for effecting operation of a portion of the compressor elements, means actuated upon movement of said motor means to a, second predetermined position for effecting operation of a second portion of the compressor elements, and means actuated upon movement of said motor means to a third predetermined position for effecting operation of all ofthe compressor elements. I

19. A system of the class described comprising, in combination, an evaporator coil for cooling air for a space to be conditioned, a compressor for supplying refrigerant to said evaporator, means in control of the flow of refrigerant through the evaporator including an expansion valve on the inlet side of said evaporator and a second valve positioned by the pressure on the outlet side of said evaporator, a control device responsive to the relative humidity of the space for additionally controlling the operation of said second valve, and

means responsive to the temperature of the space for preventing control of said second valve by said humidity cpntrol upon increase in the space temperature to a predetermined value.

20. In an air conditioningsystem for a space, in combination, cooling means for the air comprising evaporator means and variable capacity compressor means for supplying refrigerant to said evaporator means, means actuated by suction pressure in control of said cooling means to maintain the suction pressure in the evaporator means substantially constant, means responsive to the moisture in the air of said space, means responsive to the temperature of said space, connections between one of said responsive means the air passed thereover, a direct expansion refrigeration system for supplying refrigerant .to said cooling coil, means in control of the flow of refrigerant from the coil, a single motor means in control of said last mentioned means, means responsive to the pressure in the coil in control of the motor means, moisture responsive means responsive to the air being conditioned to additionally control said motor means, and means responsive to temperature for controlling said refrigerant flow controlling means irrespective of humidity when the space temperature varies to a predetermined value.

- WAYLAND R. MILLER. 

